The purpose of these investigations is to correlate the induction of fibrinogen synthesis in intact animals with alterations in the quantity and activity of the microsomal fractions derived from hepatic cells. Rabbits will receive a variety of agents known to stimulate fibrinogen synthesis. The changes in serum levels of newly synthesized fibrinogen will be compared with the quantity and activity of the polyribosomes engaged in fibrinogen synthesis. RNA prepared from polyribosomal fractions isolated by immunologic precipitation with specific antifibrinogen antibodies, will be tested for the ability to direct specific fibrinogen synthesis in a cell-free system.